1. Field of the Invention
This invention relates to liquid foaming additives used in the stimulation of oil and gas wells. The foaming additives comprise (a) a nonionic fluorochemical surfactant; and (b) a nonionic heteric polyether surfactant having at least two active hydrogen atoms.
2. Description of the Prior Art
It is known to use nonionic fluorochemical surfactants to foam lower alkyl alcohols in order to stimulate oil and gas well production. The basis for the process is that injection of the foam causes the underground formations, which are holding back the oil and gas, to break or fracture and allow the oil and gas to be released and recovered.
The problem with using nonionic fluorochemical surfactants, however, is that they are quite expensive relative to other nonionic surfactants. Consequently, researchers in the oil and gas industry, and the surfactant industry, have looked for other nonionic surfactants which could be used with fluorochemical surfactants that would reduce the cost of the foaming additive without adversely affecting the effectiveness of the foaming additive.
One type of nonionic surfactant now used in the field in conjunction with the nonionic fluorochemical surfactants is the block copolymer of an initiator having more than two active hydrogen atoms formed by the block addition ethylene oxide and propylene oxide.
Although these nonionic surfactants are effective in field use, they are solids at use temperature and must be heated in order to mix effectively with the fluorochemical surfactant and the lower alkyl alcohol to be foamed.